Abstract

Keenan and Encarnación suggest that the absence of pre-subduction inception basement in the drill core data taken from site U1438 raises ambiguity in our conclusion of spontaneous subduction initiation in the Izu–Bonin–Mariana system. However, there is no evidence for uplift in the earliest products of the Izu–Bonin–Mariana system preceding rifting preserved anywhere in the region. Three sub-parallel ridges — from north to south, the Amami plateau, Daito and Oki-Daito ridges (Fig. 1 from ref. 1) — comprise magmatic products of Mesozoic–Tertiary arcs formed prior to the Izu–Bonin–Mariana system. These ridges generally strike east–west orthogonally to the Kyushu–Palau ridge — the earliest stratovolcano chain of the Izu–Bonin–Mariana system. If compression preceded inception, as implied by the forced subduction model, we anticipate uplift of the old arc ridges, diminishing in effect westwards, and sediment shedding from uplifted regions into adjacent basins.